Tuning arrangement



Jan. 2, 1934.

O. E. DOW

vTUNING ARRANGEMENT Filed May 1e,V 1952 Patented Jan. 2, 1934 PATENT OFFICE TUNING ARRANGEMENT AOrville E. vDom-Port Jefferson, N. Y., assignor to Radio Corporation oi America, a corporation o! Delaware Application May 19, 1932. Seal No. 612,291 y 12 Claims.

This invention relates to electron discharge device circuits, and particularly to such of these circuitsl which are adapted for use with ultra high frequencies.

In the ultra short wave signalling eld wherein frequencies of the order of one hundred and fty million cycles vand upward are utilized for the communication ofl intelligence, diiliculties have been experienced in the operation of electron discharge devices. These diiiiculties are due, to a great extent, to the large inter-electrode capacity of the elements of the devices, a condition which causes energy losses in the associated tube circuits and which prevents the building up of the required high frequency controlling voltages for oscillation purposes. Great dilculty is also experienced at these high frequencies in properly tuning the circuits associated with the electrode elements of the devices for obtaining the desired controlling potentials. These diillculties are particularly noticeable in thermionlc oscillators and amplifiers.

It has been found to be essentialin order to obtain a satisfactorily high frequency output from a thermionic device at the ultra high frequencies that the cathode circuit be properly tuned. Inasmuch as most systems now in general use employ in circuits associated with the cathode circuit, choke coils whichare not variable, or else a parallel system of conductors, or-

a combination of choke coils and variable impedance circuits, a problem presents itself in tuning or adjusting vthe impedance of these circuits to a value which gives the best results.

The present invention provides a tuning arrangement especially adapted for the high frequency eld wherein the impedance of the cathode circuit of a thermionicdevice may be tuned to any desired value for effecting maximum eiliciency in the operation of the system. In accordance with the present invention the use of chokecoils which, in general, are not variable and,

-hence, not always adjusted to their best value,-

is eliminated.V 4

In general, the present invention consists in providing in the cathode circuit a metal tubingwhich has located within it and suitably spaced from its walls one or more conductors. The impedance of the circuit is varied by means of a sliding short which makes contact with the metal tubing.

(Cl. Z50-27) the invention as applied to the cathode circuit of a single electron discharge device, and

Figure 2 illustrates, schematically, the present invention as applied to the cathode circuits of a push-pull oscillator.

Figures 3 and 4 illustrate modifications of the arrangements of Figures 1 and 2, in which the two leads connecting the source of heating supyply to the cathodes .of the electron discharge devices are both located within the metal tubing,

and

. Figm'es 5 and 6 illustrate the present invention as applied to screen grid electron discharge devices.

Referring to Figure 1, there is shown an electron discharge device 1 comprising a cathode 2, an anode 3 and a control electrode 4. Cathode 2 is. energized by heating current from any suitable source of grounded supply 5 which may be either a unidirectional current source or a low frequency current source. Current over source 5 is supplied to the cathode from a circuit which may be traced from one side 6 of source 5 over inner conductor 7 of. the cathode heating circuit to one leg of the cathode. then back over the other leg to metallic conducting tube 8, and then to ground over sliding conducting strap 9 which is made movable over the surface 4of tube 8. This adjustable strap 'enables' the tuning of the impedance of the cathode heating circuit to any desired value. A

Concentric conducting tube 8 is insulated from the inner conductor '7 and is arranged to support the inner conductor in any suitable manner, such as by porcelain or glass beads, or other insulating spacers. If desired, the inner conductor may be merely an insulated conductor.

By meansfxof this-:arrangement of inner and outer conductors, both act together as a single conductor for the high frequency currents. To aid in securing this effect, by-pass condenser 10 is provided across the legs of the cathode proper. Due to the position of the conductors the reactance ofthe inner conductor 'I to the high frequency currents is much higher than that of the outer conductorv to the same currents, and, consequently, the` ultra high frequencies are confined mainly to the outer conductor 8.

Figure 2 illustrates one manner of applying the present invention to a push-pull oscillator or amplifier circuit. An arrangement of this type is utilized and described in a copending application of N. E. Lindenblad, Serial No. 603,310, filed April 5, 1932;

In this figure, the cathode heating circuit may be traced from lead 11- through short circuiting or conducting strap 12, through conducting tubes 13 and 14, through the respective legs of the cathode elements of the electron discharge tubes 15, 16, and back over the inner insulatedconductors 17, 18 to the other lead 19. For tuning the heating circuit, short circuiting strap 20 is made movable along the tubes 13 and 14. Obviously; if desired, conducting strap 12 may be eliminated and conductor 11- connected directly to short circuiting strap 20.

By-passing condensers 21 and 22 are provided for the conductor system 13, l'I'and 14, 18. respectively, and connected in the circuit in the same manner as indicated in Figure 1.

If desired, both leads supplying heating current to the legs of the cathode may be located within the metal tubing, as shown in Figures 3 and fi. Such an arrangement is particularly advantageous when the cathodes are heated by an alternating current source, and it is desired to have the tuning short-designated by reference character 9 in Figure 3 and 20 in Figure 4-at ground potential with respect both to the radio frequency voltage and the voltage of the heating source. The metallic tubing now conducts only ultra high frequency currents.

Where it is desired to employ four element or screen grid electron discharge devices at ultra 'high frequencies the circuits shown in Figures 5 and 6 may be used. The voltage supply for the screen grid electrode 21 may be connected, as shown in Figure v5, to the tubular conductor which, in turn, is connected to the screen grid. An alternative arrangement is shown in Figure 6 where the screen grid electrode 21 of each device is fed by a third conductor 22 also located within the tubular conductor together with the cathode heating conductors.

From the foregoing, it will be apparent that numerous other modifications may be made in the circuit without vdeparting from the spirit and scope thereof. .Forexampla a telescopic tube arrangement may easily be employed instead of Athe xedtubular conductor.

' What is claimed is:

' 1. High frequency apparatus in combination an electron discharge device, a cathode electrode for said device, a source of energizing current for heating said cathode, a connection extending between. said source and said cathode electrode, and a conducting tube associated with said cathode electrode surrounding at least a portion of Vsaid connection, and a tuning strap arranged to be adjustable over the surface of said conducting tube.

2. An energizing circuit for the cathode of an electron discharge device comprising a source of heating' current and connections from said source to the legs of said cathode comprising a tubular' lconductor conne'cted to one of said legs, and a conductor within said tube and insulated therefrom connected to the other of said legs and a grounded tuning element in contact with said tubular conductor and adjustable with respect to the ends thereof.

3. A circuit as described in claim 1 including a condenser across the legs of said cathode.

4. An energizing circuit for the cathode of an electron discharge device comprising a source of heating current, and connection.. from. lsaid source to the legs of said cathode comprising a conducting tube connected to one of said legs. and a. conductor within said vtube and insulated therefrom connected to the other of said legs,

and a tuning strap arranged to be adjustable over the surface of said conducting tube.

5. Ultra high frequency apparatus having, in combination, an electron discharge device, a cathode electrode for said device, a source of energizing current for heating said cathode, and connections extending between said source and said cathode electrode, said connections comprising a tunable metal conducting tube containing within it a conductor insulated from said tube.

6^. Ultra high frequency apparatus having, in combination, an electron discharge device, a cathode electrode for said device, a source of energizing current for heating said cathode, individual conductors connecting said source and legs of said. cathode electrode, one of said conductors comprising a tunable metal conducting tube, and the other conductor comprising a wire within said tube and insulated therefrom.

'7. A push-pull circuit having, in combination, two electron discharge devices, individual cathodes for said devices, a source of energizing current for said cathodes. connections from said source to said cathodes connecting vsaid cathodes in parallel relation in respect to said source, said connections vincluding a tubular conductor associated with each of said cathodes, each of said tubular conductors being connected to one leg of its associated cathode, and leads Vcontained within said tubular conductors but insulated therefrom and associated with the otherleg of each of said cathodes, and a tuning element-electrically connecting together said tubular conductors and adjustable with respect to the ends thereof.

8. Ultra high frequency apparatus having, in combination, a push-pull oscillator comprising two electron discharge devices, individual cathodes for said devices, a source of energizing current for said cathodes, connections from said source to said cathodes connecting said cathodes in parallel relation in respect to said source, said connections including a tubular conductor associated with each of said cathodes, each of said tubular conductors being connected to one leg of its associated cathode; and leads contained -within said tubular conductors but insulated therefrom and. associated with the other leg of each of said cathodes, and'a tuning element electrically connecting together said tubular conductors and adjustable with respect to the ends thereof, and condensers connecting together the legs of each of said cathodes.

9. An energizing circuit for the cathode of an electron discharge device comprising a source of heating current, conductors extending from' said source to the legs of said cathode, a conducting tube surrounding at least a portion of said conductors, a capacitive connection across the legs of said cathode, another connection from the electrical mid-point of said capacitive connection to said tube, and a tuning strap arranged to be adjustable over the surface of said conducting tube.

10. High frequency apparatus having, in combination, an electron discharge device including a screen grid and a cathode electrode, a source of heating current, conductors extending from said source to the legs Aof said cathode, a conducting tube surrounding at least a portion of said conductors and connected to said screen grid, a capacitive connection across the legsof said cathode, another connection from the electrical mid-point of said capacitive connection to said tube, and a tuning strap arranged to be adjustable over the surface of said conducting tube;

11. A push-pull circuit having, in combination. two electron discharge devices, individual screen grid electrodes and cathodes for said devices, a source of energizing current for said cathodes, conductors extending from said source to said cathodes connecting said cathodes in parallel relation in respect to said source, a metal conducting tube individually associated with each of said cathodes and arranged to surround at least a portion of both of said conductors and insulated therefrom, each of said conducting tubes being connected to the screen grid electrode of its associated electron discharge device,l a

capacitive connection across the legs of each of said cathodes, and a tuning element electrically connecting together said tubular conductors and adjustable with respect to the ends thereof.

l12. High frequency apparatus having, in' combination, an electron discharge device, a cathode electrode. for said device, a source of energizing current `for heating said cathode, a connection extending between said source and said cathode electrode, and a tunable conducting tube associated with said cathode electrode and surrounding at least a portion o1' said connection.

ORVILLE E. DOW. 

